Should I get another dog ?

Well my dog just passed away on june 29 at 2:32 am and I would like to know should I get another one for her sister to play with and would she be happy and how long will it take her to get back to normal ? The one who just passed away of cancer was 12 years old and her sister who is a lab is around 9 or 10 years old and is over weight , yes i exercise her but would it help her lose some Weight with another dog ?